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Fibre Channel (SAN)

Regular Contributor
Posts: 166
Registered: ‎02-05-2014

Re: counters tim_txcrd_z increase

Hmm, I learn new things here all the time or they are absolute nonsense. I preffer to think the latter.


First a comment by Eli:

Each frame can "live" in the queue 2.5us, and after this timeout the frame discarded."


If that was the case not a single frame would ever reach an HBA or Storage target. 2.5 microseconds is the measuring interval where the ASIC checks on the amount of credits. If it is 0 at that particulate point in time this counter increments by one. The time a frame can live inside a receive buffer is determined by the hold-time which is either 220ms, 500ms or a user defined value.


See here on a very nasty trap if you get this wrong:



Buffer credits are defined by the receiving side of a port. That means that during FLOGI and the Accept on that FLOGI the two port tell eachother how much buffers they have/allow the remote side to send without having to obtain an R_RDY primitive.



See here:

and here



Kind regards,
Erwin van Londen
Brocade Distinguished Architect The Fibre Channel blog

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